The present invention relates to adhesion promoters for addition-curable silicone compositions.
As shown in U.S. Pat. No. 3,284,406, the adhesion of a cured platinum catalyzed addition-curable silicone composition onto a substrate is improved by effecting the cure of the silicone composition at a temperature such as 100.degree. C. for at least one hour.
U.S. Pat. No. 5,164,461, which is incorporated herein by reference, is directed to the use of certain silylalkyl maleates, silylalkylmaleimides and silylalkyl fumarates, such as bis[3(trimethoxysilyl)alkyl]fumarates, as adhesion promoters in addition-curable silicone adhesive compositions. Although these silicone compositions are self-bonding to various substrates, such as plastics, metals and glass, they also require a temperature of about 100.degree.-150.degree. C. to effect a satisfactory cure.
It would be desirable, therefore, to provide an addition-curable silicone adhesive composition which could be applied onto an unprimed substrate, such as plastic or metal, to effect a satisfactory cure in less than an hour and at a temperature of less than 100.degree. C. In addition, it also would be desirable to produce a silicone substrate composite having a silicone layer which would fail cohesively instead of adhesively when tested. As used hereinafter, the expression "adhesive failure" means the silicone layer can be cleanly separated from the substrate, while in a "cohesive failure", rupture can occur in the silicone layer or in the substrate when separation is attempted.